The design of future parallel computers requires rapid simulation of target designs running realistic workloads. These simulations have been accelerated using two techniques: direct execution and the use of a parallel host. Historically, these techniques have been considered to have poor portability. This paper identi- ﬁes and describes the implementation of four key oper- ations necessary to make such simulation portable across a variety of parallel computers. These four operations are: calculation of target execution time, simulation of features of interest, communication of target messages, and synchronization of host proces- sors. Portable implementations of these four operations have allowed us to easily run the Wisconsin Wind Tun- nel II (WWT II)—a parallel, discrete-event, direct-exe- cution simulator—across a wide range of platforms, such as desktop workstations, a SUN Enterprise server, a cluster of workstations, and a cluster of symmetric multiprocessing nodes. We plan to release WWTII in August, 1997. We also plan to port WWT II to the IBM SP2. We ﬁnd that for two benchmarks, WWT II demon- strates both good performance and good scalability. Uniprocessor WWT II simulates one target cycle of a 32- node target machine in 114 and 166 host cycles respec- tively for the two benchmarks on a SUN UltraSPARC. Parallel WWT II achieves speedups between 4.1-5.4 on 8 host processors in our three parallel machine conﬁgura- tions.